1. Field of the Invention
This invention relates to the atomization of liquids by means of a vibrating perforated member, such as a membrane or an orifice plate. More particularly the invention concerns the control of liquid flow through such orifice plate to ensure a stable and continuous atomizing operation.
2. Description of the Related Art
Vibratory atomizing devices are well known, as seen for example, in U.S. Pat. No. 5,152,456, U.S. Pat. No. 5,164,740, U.S. Pat. No. 4,632,3171 and U.S. Pat. No. 4,533,082. In general, such devices incorporate a thin plate having at least one small orifice extending therethrough and which is attached to and vibrated by a piezoelectric actuation element. An alternating voltage applied to the piezoelectric actuation element causes it to expand and contract; and this expansion and contraction produces up and down vibratory movement of the orifice plate. A liquid supply, such as a wick, transports liquid to be atomized from a reservoir to the one side of the plate so that the liquid contacts the plate in the region of its perforations. The up and down vibratory movement of the plate pumps the liquid through the orifices and ejects the liquid as aerosolized liquid particles from its upper surface.
One particularly efficient piezoelectric atomizing arrangement uses an annularly shaped piezoelectric actuation element having a central opening and an orifice plate that covers the central opening on the piezoelectric element. The plate extends across and somewhat beyond the central opening of the piezoelectric actuation element; and it is fixed to the element where it overlaps the region of the element around its central opening. When an alternating voltage is applied to the upper and lower sides of the piezoelectric actuation element, the element expands and contracts in a radial direction. This radial expansion and contraction increases and decreases the diameter of its central opening, which in turn forces the orifice plate to flex and bend so that its central region, which contains one or more orifices, moves up and down in a vibratory manner.
Preferably, the orifices are formed in the central region of the plate and this region is domed slightly.
A problem occurs in these piezoelectric vibratory atomizer devices in that not all of the liquid which is pumped through the perforations in the orifice plate becomes ejected from the upper surface of the plate. The liquid which is not ejected or ejected liquid which falls back on the plate remains on the upper surface of the plate and interferes with the atomizing action. Further, in the situation where the orifice plate is attached to the underside of the piezoelectric element, the liquid which is not ejected and accumulates in a well which is formed by the central opening of the piezoelectric actuator element and the underlying plate. Eventually this accumulated liquid builds up to a degree such that it damps the pumping action and decreases the output of atomized liquid particles.
The use of drain holes and reflux channels to drain excess ink from nozzle plates is described in U.S. Pat. No. 4,542,389 and U.S. Pat. No. 4,413,268. However, these nozzle plates neither vibrate nor do they convert radial actuator movements to up and down vibratory movements of a perforated orifice plate. Moreover, a wick is not used to transfer liquid to these nozzle plates.
In one aspect the present invention involves a novel atomizing device which comprises a generally horizontally extending plate having an elevated region adjacent a lower region and formed with at least one atomizing orifice in the elevated region and at least one drain opening in the lower region. The drain opening is substantially larger than the atomizing orifice and permits liquid to flow freely therethrough. The atomizing device also includes a vibration actuator which is connected to vibrate the plate up and down as well as a liquid conductor which is arranged to conduct liquid from a reservoir to the underside of the elevated region of the plate. The liquid which is not ejected from the atomizing orifices in the elevated region or which falls back on the plate flows down to the lower region and through the drain opening.
In another aspect, this invention is based on the discovery that by providing one or more openings in the vibrating plate in a region away from the atomizing orifices, but. over the upper end of the wick or other capillary type liquid conductor means, the liquid which passes down through the openings will tend to saturate the upper end of the liquid conductor means and diminish its drawing power. As a result, the liquid conductor means will stop drawing further liquid from the reservoir and will instead direct the liquid which has passed through the openings back up under the atomizing orifices in the central region of the vibrating orifice plate. This recycled liquid is re-pumped through the atomizing orifices by the continued up and down vibration of the plate and is ejected from the upper surface of the plate.
As the recycled liquid is atomized, the upper end of the wick or liquid conductor means becomes less saturated and it is thereby enabled to draw additional liquid up from the reservoir.
According to this aspect of the invention, a plate having at least one atomizing orifice is caused to vibrate while a liquid is supplied via a capillary type liquid conductor element, such as a wick, which extends from a liquid reservoir. The capillary action of the liquid conductor element causes liquid to be drawn from the reservoir and supplied to the lower side of the plate in the region of the orifice. The vibration of the plate causes the liquid to be pumped through the orifice and ejected from the other side of the plate in the form of aerosolized liquid particles.
The plate is also formed, in a region displaced from the atomizing orifice, with at least one larger opening through which liquid which had not been ejected from the plate or which falls back on the plate can freely flow. This larger opening is located in a position such that it directs the liquid which flows through it to the upper end of the liquid conductor element where it comes into capillary communication with the atomizing orifice on the under side of the plate. This nonejected liquid or liquid which has fallen back on the plate tends to saturate the upper end of the liquid conductor element such that it diminishes the ability of the element to draw additional liquid from the reservoir. As a result, the liquid conductor element draws less or no liquid from the reservoir and instead, by means of capillary action, directs the liquid which has passed through the openings back under the atomizing orifice in the vibrating orifice plate. This recycled liquid is re-pumped through the atomizing orifice by the vibration of the plate and is ejected from the upper surface of the plate in the form of finely divided liquid particles.
The returned liquid which is directed by the liquid conductor element tends to increase the saturation of the element and thereby restricts the element""s ability to supply additional liquid from the reservoir, at least until the returned liquid has been re-atomized. This provides an automatic regulation effect on the liquid conductor element, which prevents flooding and waste of the liquid being atomized.
According to a further aspect of the invention there is provided a novel method of atomizing a liquid. This novel method comprises the steps of providing an orifice plate having at least one atomizing orifice, vibrating the plate, at least in the region of the atomizing orifice, while delivering a liquid by capillary action through a capillary type liquid conductor element extending from a liquid reservoir to a location adjacent the atomizing orifice on one side of the plate. The liquid is caused to be pumped through the atomizing orifice and ejected from the other side of the plate in the form of aerosolized liquid particles by the vibration of the plate. The liquid which has not been ejected from the plate, or which falls back on the plate, is directed to flow back down through at least one larger opening in the plate at a location displaced from the atomizing orifice. This non-ejected liquid is conveyed by capillary action back to the atomizing orifice on the one side of the plate for further atomization. Also, this non-ejected liquid acts on the liquid conductor element in a manner to restrict its ability to draw additional liquid from the reservoir until the non-ejected liquid is again pumped through the orifice and ejected from the plate.